1. Field of the Disclosure
The present disclosure relates to a keyless entry apparatus that performs locking/unlocking of doors and so forth by performing wireless communication between a vehicle-side device and a mobile device, and, in particular, to a mobile device for a vehicle that can cause a vehicle-side device to determine, with a high accuracy, whether the mobile device is positioned inside or outside the vehicle.
2. Description of the Related Art
A keyless entry apparatus is known, which performs wireless communication between a vehicle-side device provided in a vehicle and a mobile device carried by a user, and which performs locking/unlocking of doors of the vehicle. Furthermore, a passive keyless entry apparatus is known, which automatically performs, when a mobile device is moved close to a vehicle, communication between a vehicle-side device and the mobile device, which authenticates an identification (ID) that is specific to the mobile device, and which performs operations of locking/unlocking doors of the vehicle.
The above-mentioned passive keyless entry apparatus is required to be capable of determining whether the mobile device exists outside or inside the vehicle. For this reason, in the vehicle-side device, portions of the vehicle are provided with a plurality of transmitting antennas. The mobile device detects the signal strengths of signals that are received from the individual transmitting antennas. The position of the mobile device is calculated using information items indicating the signal strengths, and whether the mobile device is positioned inside or outside the vehicle is determined (for example, see Japanese Unexamined Patent Application Publication No. 2008-266955).
Regarding a keyless entry apparatus described in Japanese Unexamined Patent Application Publication No. 2008-266955, a vehicle-side device is provided with a vehicle-side transmitting unit that is connected, via signal lines, to a plurality of transmitting antennas for transmitting request signals, and a vehicle-side receiving unit that receives answer signals. Furthermore, a mobile device is provided with a mobile-device receiving unit that receives the request signals, a mobile-device transmitting unit that transmits the answer signals, and a mobile-device control unit that detects individual signal strengths of signals which are transmitted from the transmitting antennas of the vehicle-side device. When the signal strengths of the signals transmitted from the transmitting antennas are detected by the mobile-device control unit and the sum of distances calculated using two data items among data items indicating the signal strengths is smaller than a predetermined threshold, the vehicle-side control unit or the mobile-device control unit determines that the mobile device is positioned inside the vehicle.
However, regarding the keyless entry apparatus described in Japanese Unexamined Patent Application Publication No. 2008-266955, in a case in which the mobile device is positioned in the vicinity of a signal line that is disposed in the vehicle, and in which a signal emitted from the signal line is received as noise by the mobile device, erroneous determination of whether the mobile device is positioned inside or outside the vehicle can be prevented. However, there is a problem that the erroneous determination caused by noise cannot be prevented in a case in which the mobile device exists outside the vehicle.